1. Field of the Invention
The present invention relates to a piezoelectric resonator and a piezoelectric filter.
2. Description of the Related Art
In general, a piezoelectric resonator is configured such that a thin-film portion in which a piezoelectric film is sandwiched between an upper electrode and a lower electrode is arranged on a substrate, and a vibration section in which the upper and lower electrodes overlap with each other is acoustically isolated from the substrate. Heat is generated in the vibration section.
For example, Japanese Unexamined Patent Application Publication No. 2004-120219, as shown in FIG. 17 which is a plan view and FIG. 18 which is a sectional view taken along a line A to A of FIG. 17, discloses a technique of improving a heat-radiating property and an electric-power resistance by forming a heat-radiating film 118 in a portion, except for a vibration portion 111b, of a piezoelectric resonator having a substrate subjected to through-etching from a back surface thereof so that a space 110a is formed. That is, a lower electrode 114 which has a substantially cross shape in a plan view and which includes a base portion 114a, a tip portion 114b, and wing portions 114c, a piezoelectric thin-film 115, an upper electrode which has a projecting shape in a plan view and which includes a base portion 116a and a tip portion 116b which have different widths, and the heat-radiating film 118 are arranged on an SiO2 film 111 which is formed on a first main surface of the substrate 110. The vibration portion 111b corresponds to a portion in which the tip portion 114b of the lower electrode 114 and the tip portion 116b of the upper electrode 116 overlap each other (i.e., a hatched portion in FIG. 17). Note that a Si2 film 112 arranged on a second main surface of the substrate 110 is removed in a step of manufacturing.
However, since the upper electrode 116 is exposed in an opening 118a provided in the heat-radiating film 118 with a gap between the heat-radiating film 118 and the exposed upper electrode 116, and the heat-radiating film 118 is arranged so as to be isolated from the vibration section 111b which defines a heat-generation source, heat conduction is degraded due to the gap between the vibration section 111b and the heat-radiating film 118, which results in a degraded heat-radiating property. Furthermore, deterioration of a Q factor occurs due to unnecessary vibration in the piezoelectric resonator, and the deterioration of the Q factor causes heat generation. Therefore, in order to improve electric-power resistance, the heat-radiating property is improved and the unnecessary vibration is prevented from occurring so that the heat generation due to the deterioration of the Q factor is prevented.